This invention relates to a catalytic system for polymerizing olefins, a novel component of the system containing titanium halide, a process for preparing the novel component containing titanium halide, and the use of the system in polymerizing olefins, especially propylene.
The polymerization of olefins by heterogeneous complex catalytic systems, often termed Ziegler-Natta catalysis, has been well-known for over 25 years. Generally, there are two components in this type of system: one based on an organoaluminum compound or its substitute, the other containing a titanium or other transition metal halide. Although thousands of such catalytic systems have been disclosed, there is always a quest for improvement in two important properties: activity and isotactic index.
Activity is measured by the grams of polyolefin produced per gram of titanium component or other transition metal component employed in the catalytic system. The higher the activity, the lower the amount of metallic ash and corrosive halide left in the polymer. If the activity is high enough, e.g. .gtoreq.6,000, then the de-ashing step in processing the final polyolefin can be omitted--an important improvement.
For olefins, such as propylene, which can form isotactic structures, the higher the isotactic index, the better the physical properties of the polymer. Isotactic polypropylene is more ordered, less soluble in halocarbons or hydrocarbons, and useful for its higher strength than the more soluble atactic form. Isotactic indices of 93 or higher are favored for commercial polypropylene.
Previously Kashiwa et al. disclosed in U.S. Pat. No. 3,642,746 a process for polymerizing olefins by means of a catalytic component supported on a metal dihalide, which has been treated with an electron-donor compound and then reacted with either titanium tetrachloride or vanadium tetrachloride. Among the electron-donor compounds are aliphatic and cyclic ethers.
U.S. Pat. No. 4,145,313 granted to Langer discloses TiCl.sub.4 supported on MgCl.sub.2 and one or more Lewis bases, among which ethers are named, as catalysts and branched secondary or tertiary trialkylaluminum compounds and other organometallics as cocatalysts. Ethers may also be complexed with the cocatalysts.
Similarly U.S. Pat. No. 4,279,776 granted to Shiga et al. discloses a three-component catalyst system wherein component A, an organomagnesium compound, is synthesized in the presence of an ether, is then caused to react with a halogen-containing compound of silicon or a halogeno-aluminum compound to form a solid product, which is caused to react with an electron donor selected from one of twelve classes of compounds, one of which is an ether, and then caused to react with TiCl.sub.4 ; component B is an organoaluminum activating agent; and component C is an electron donor selected from one of twelve classes of compounds, one of which is an ether.
U.S. Pat. No. 3,888,835 granted to Ito discloses a catalyst system comprising a copulverized catalyst of TiCl.sub.4 or TiCl.sub.3 material, and aluminum halide-ether complex, and magnesium halide employed with an organoaluminum cocatalyst. The aluminum halide-ether complex is said to cause marked diminution of the surface area of the catalyst component.
All four of the disclosures above are incorporated by reference into this application.
It is an object of this present invention to provide a catalytic system for polymerizing olefins, such as propylene, so active that de-ashing may be omitted and so constituted that polymer with a high isotactic index is produced. Other objects of this invention will be apparent to those skilled in the art.